This mod will enable the TS-870S to transmit on MARS, CAP and other frequencies.
Here is your chance to prove how adept you are at microsurgery.
1. Remove top and bottom covers.
2. Remove the top screw from each side of the front panel assembly.
3. Carefully rotate the front panel forward to gain access to the control board(x53-3560-11 a/4).
This board is mounted vertically against the body of the transceiver. It is not the board that is mounted in the front panel assembly.
4.
Locate and remove resistor R244 from the
control board. R244 is below IC12 ROM and above IC23. There are two chip
resistors,
one on top of the other -carefully remove or break the top
one..it is easily fractured -that's R244.
5. Reassemble and then perform the cpu reset by
holding the A=B button depressed as power is turned on.
(Source: www.Ham.dmz.ro)